76 



University of 



California. 



[Vol. 3 



The specimen of perrini shows the greater portion of the 

 caudal region well preserved, and furnishes some interesting evi- 

 dence concerning the character of the tail fin . The middle portion 

 of the tail seems to be somewhat wider or higher than that 

 of Ichthyosaurus, owing to the length of the haemal spines, 

 and was, consequently, more effective as a sculling organ. 

 As is shown in Plate 5, fig. 1, the posterior portion of the 

 caudal series is quite sharply deflexed, and evidently extended 

 into the lower lobe of a fin like that now known to have existed 

 in Ichthyosaurus. The bend in the caudal series is present at the 

 place where it occurs in Ichthyosaurus , and as other portions of 

 the vertebral column have not suffered much disturbance, it is 

 probably due to normal curvature in the vertebral column of the 

 living animal. 



Arches. — The pectoral girdle of Shastasaurus is represented 

 by a nearly complete arch in a specimen of alexandne (PI. 12) 

 and the greater portion of a girdle belonging to osmonti (PI. 10, 

 fig. 1). Both specimens show this arch to be formed essentially 

 as in Ichthyosaurus. In the specimen of alexandrce the arch lies 

 on the top of the partly inverted cervical vertebras. The left 

 scapula and coracoid are brought into the same plane, while on 

 the right side the scapula was doubled under the coracoid. The 

 distal ends of the coracoids almost touch, and the left clavicle lies 

 in front of the coracoid on that side. Being very slightly dis- 

 turbed and above the partly inverted vertebrae, it is evident that 

 it is the inferior surfaces of the arch bones that are exposed. 

 As the superior side of the skull is uppermost, the body probably 

 first lay on its side, aud, in crushing down, the head turned 

 slightly, coming into a horizontal position. 



From this specimen the mutual relations of all of the arch 

 bones can be made out with absolute definiteness. In the speci- 

 mens of osmonti the elements, although not advantageously 

 placed for study, were associated with the anterior limbs and 

 cervical vertebras and certainly belong to one individual. 



The coracoids are quite different from the element figured 

 with the original description of the genus. The bone which the 

 author and others* supposed to be the coracoid has little in 



* Dames, Frass. See Dames 1895, p. 1049. 



